This invention relates generally to rotary machines and more particularly, to bling assemblies for use in a rotary machine.
At least some known steam turbines have a defined steam path which includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. Many of these steam turbines include stationary nozzle segments that channel a flow of steam towards rotating buckets, or turbine blades, that are coupled to a rotatable member. At least some known stationary nozzle segments include a plurality of airfoils that facilitate channeling the steam flow. Each nozzle segment, in conjunction with an associated row of buckets, is usually referred to as a turbine stage and most known steam turbines include a plurality of stages.
Some known steam turbines have a semi-circular radially outermost portion, sometimes referred to as a shroud, that is coupled to a semi-circular airfoil portion. Such airfoil portions are generally assembled by coupling a plurality of airfoils to a semi-circular band that is inserted into a dovetail groove defined within the shroud. Because the different steam turbine components may have been formed with differing manufacturing processes, specifications, and/or tolerances, the components may be assembled with cumulative dimensional deviations, known as stack-up tolerances, that may exceed overall tolerances. Because stack-up tolerances may increase manufacturing costs and/or reduce steam turbine efficiency, generally the tolerances of individual components may need to be decreased to facilitate mitigating any stack-up tolerances which may be created during assembly.
Moreover, some known steam turbines include airfoils that have been inserted within the assemblies with a pre-twist. The pre-twist induces predetermined stresses into the associated airfoils that facilitate absorbing and dampening dynamic stresses that may be induced during operation, while reducing long-term airfoil wear and misalignment. However, minute variances in the associated tooling and manufacturing environments may increase the difficulty in maintaining stringent process control tolerances in forming the aforementioned pre-twist and may outweigh any benefits that may be provided with the pre-twist.